Engine loses power at highway speed after 15 minutes - clicking sound, rough engine

[BHBITB]

Driving under 3500 RPM is fine but at highway speeds it runs rough after 15 minutes. Turning the engine off for a minute or two solves the issue until it is at speed again. There is a clicking sound that is noticeable when it is running rough.

I have been trying to diagnose this problem and have tried a number of things (I think the problems are compounded as it has gotten better with some fixes). I have replaced the spark plugs recently (before the issue) New alternator, new Catalytic Convertor. Belts are good, new oil. I ran some sea foam through

I wonder if it is fuel injector or distributor cap. hope its not in the engine

Any ideas?

[originalkwyjibo]

Check/change fuel filter. If there is sediment in the tank, it may be stirring up and clogging the filters. When you shut it off for a few minutes it will settle. Start up and drive again it stirs back up. If the filter is full of sediment then you may need to flush the fuel tank as well.

[BHBITB]

thanks! I ordered the filter and plan to install this weekend. I am also replacing the TPS for good measure as the van has about 120K on it. Hopefully this solves it

[BHBITB]

HELP!
The van is still losing power and running poorly when driven at hard highway speeds for ~15 minutes. When it gets rough the engine almost sounds like a diesel with a clicking sound. I can drive it around all day if I keep the RPM’s around 2-3k.

I replaced the fuel filter and the TPS and cleaned out the throttle body. When the van sits for 5-10 minutes the problem “resets" and the van can be driven normally (not at highway speeds). I really thought i had it this time. My battery died in the process which confused me for a minute.

Now I am wondering if it is an exhaust issue - I installed a new cat but am looking at the EGR components. I couldn’t find any exhaust leaks when I did a simple test with backflow and soapy water

or a sensor issue

I have been following this thread and might try these components: https://www.toyotavantech.com/forum/showthread.php?400-Van-sputter-and-hesitation-after-hauling-a/page3&highlight=EGR+modulator

[BHBITB]

Also - I have not had any codes which adds to my confusion

[Jan-Willem]

Hi, sorry, i do not have the answer for you, i have been thinking about it, but it is a weird combination of things, which makes me think of the most horrible thing. One thing is different to my van, mine does not nearly do 3500 rpm at highway speeds. How fast are you going?
Did the issue start before or after you changed the oil? I can imagine that if the engine lose lubrication at high rpm, because of low oil or wrong viscosity, that it will eventually start ticking and lose power. And that it returns to normal when the oil returns to the pan. But that would not be a good thing, so i very much hope that that is not the reason!

[BHBITB]

It will do 60-70 MPH (~100km) for 10-15 minutes

It did start after an oil change but it is my normal guy so nothing changed there.

When you say”the most horrible thing” what exactly are you referring to?

[Jan-Willem]

Well, if there the oil is very thin, or there is not enough of it, so much so, that the valves get oil starvation, you will get a lot of tapping noise from the valve train. If you continue to drive it, it will cause power loss as well, either because of friction of the engine, or friction that prevents valves from closing properly. But that is really bad for the engine, friction=wear, and tapping means hard contact, which is wear.
It would explain the symptoms, but what I find hard to believe, is, that this can actually occur multiple times, without destroying the engine, and also I would expect other warning signals as well, the oil pressure meter dropping, oil light coming on, a pronounced hot-engine-smell.

Another thought I had, is that maybe the fuel pump does not provide enough fuel, like it was suggested in the first reply, maybe because it is pulling a vacuum on the tank, because the vent is blocked. But then again, you would sort of expect that would be a massive issue with a full tank, and not so much with an empty tank. Not enough fuel creates a lean condition, which would create knocking. And this would be easy to test if you open the fuel cap a bit when the issue occurs.

By the way, mine doesn't nearly do 3500rpm at 100kmh (62mph), maybe 2700 ? But these probably came with different gearings, and i have no idea if my differential is original.

[Jan-Willem]

https://spicerparts.com/calculators/transmission-ratio-rpm-calculator
https://carfromjapan.com/specifications/toyota/townace-wagon/581339d32afaa2c4b2867fc0
If you enter the transmission ratio's, the final drive ratio, and the wheel diameter 24.5-25inch, you can calculate the correct RPM for each gear and speed.
3500 at 60-ish, that is 3rd gear on an auto box, or 4th on a manual. With the overdrive engaged it should be more like 2500RPM at that speed.

[BHBITB]

thanks for the insight - I wouldn’t say that the van stays at the lower RPM at highway speeds once it is cruising. I have been driving it hard to try to recreate the issue after I “fix” something. I will check the oil, I have avoided the fuel pump because I hear it is difficult to replace but everything on this van has a degree of difficulty so nothing new there.

I recently replaced the spark plugs and wires - I might go back and double check those because now I am second guessing everything I have done to the van

[Jan-Willem]

The fuel pump is not so hard, but still, I wouldn’t unless you are sure it is the pump. It is easier and cheaper to measure the fuel pressure. Plus no guarantee that the new fuel
pump is good or reliable, unless you get an an oem or a quality/expensive one.
I dropped the tank a couple of times to get a sender to work properly. it was an expensive affair, because when I saw the condition the insides, i had it sandblasted and coated.

here is a thread explaining how to measure the pressure:
https://www.toyotavantech.com/forum/content.php?222-Testing-fuel-system-replacing-fuel-pressure-regulator
I did it a bit differently myself. I swapped the top banjo bolt for one with a pressure sender/gauge connector, and threaded a pressure gauge directly in it, and just left it there.